The present invention relates to a process for producing a modified diene polymer rubber superior in impact resilience and processability. The modified diene polymer rubber is most suitable as a fuel cost saving rubber used for motorcar tires because of its superior impact resilience.
A styrene-butadiene copolymer obtained by emulsion polymerization is known as rubber used for motorcar tires. However, said copolymer has a problem that motorcar tires comprising said copolymer are not satisfactory from a viewpoint of fuel cost saving, because the copolymer is insufficient in its impact resilience.
In order to obtain rubber superior in its impact resilience, JP-A60-72907 discloses a process, which comprises copolymerizing butadiene and styrene in a hydrocarbon solvent using an organolithium compound as an initiator, and a Lewis base such as ether as a microstructure controlling agent.
Further, Japanese Patent No. 2540901 proposes a process, which comprises reacting an alkali metal, which is bound at the end of a diene polymer rubber, with a specific acrylamide to obtain a modified diene polymer rubber having improved impact resilience.
Furthermore, Japanese Patent Application No. 2000-328813 discloses a process, which comprises reacting an alkali metal, which is bound at the end of a diene polymer rubber, with a specific amine to obtain a modified diene polymer rubber having improved impact resilience and processability.
However, recently, a level of a demand for fuel cost saving of motorcar tires, and for processability of rubber is high, and therefore, any of the above-mentioned copolymer rubbers can hardly meet such a demand.
An object of the present invention is to provide a process for producing a modified diene polymer rubber superior in impact resilience and processability.
The present invention provides a process for producing a modified diene polymer rubber, which comprises the steps of:
(i) polymerizing a conjugated diene compound, or a combination of a conjugated diene compound and an aromatic vinyl compound in a hydrocarbon solvent in the presence of an alkali metal catalyst, thereby obtaining an active conjugated diene polymer having an alkali metal at the end thereof; and
(ii) reacting the active conjugated diene polymer having an alkali metal at the end thereof with an amine compound represented by the following formula (1), thereby obtaining the modified diene polymer rubber, 
wherein each of R1, R2 and R3 is an alkyl group having 1 to 8 carbon atoms, R4 is an alkoxy or alkyl group having 1 to 8 carbon atoms, and n is an integer of 1 to 8.
The present invention also provides a process for producing a modified diene polymer rubber, which comprises the steps of:
(i) polymerizing a conjugated diene compound, or a combination of a conjugated diene compound and an aromatic vinyl compound in a hydrocarbon solvent in the presence of an alkali metal catalyst, thereby obtaining an active conjugated diene polymer having an alkali metal at the end thereof; and
(ii) reacting the active conjugated diene polymer having an alkali metal at the end thereof with an amine compound represented by the above formula (1) and a silicon or tin compound represented by the following formula (2), thereby obtaining the modified diene polymer rubber,
RaMXbxe2x80x83xe2x80x83(2) 
wherein R is an alkyl, alkenyl, cycloalkenyl or aromatic hydrocarbon group, M is a silicon or tin atom, X is a halogen atom, a is an integer of 0 to 2, and b is an integer of 2 to 4.
The modified diene polymer rubber obtained in the above-mentioned latter invention is further superior in processability to that obtained in the above-mentioned former invention.